The present invention relates to an actuating unit for a hydraulic brake system for automotive vehicles, including a pneumatic brake power booster, which is preferably a vacuum brake power booster, and a master brake cylinder inserted after the brake power booster in terms of effect. The brake power booster includes a booster housing, the interior of which is subdivided into two chambers by a movable wall which is attached to a control housing accommodating a control valve, and a centrally arranged force-transmitting element being provided which is in force-transmitting connection with the master brake cylinder, on the one hand, and a vehicle body wall of the automotive vehicle, on the other hand.
An actuating unit of this type is disclosed in German patent DE 29 22 299. The force-transmitting element of the brake power booster of the prior-art actuating unit is provided as a carrying pipe with axial slots, through which the movable wall is coupled with a part of the control housing which is arranged inside the carrying pipe and actuates an output member transmitting the output force of the brake power booster.
What is considered least favorable in the referenced actuating unit is the complicated and costly way of transmitting forces from the movable wall to the output member, which is done by means of tabs provided on the movealble wall to the above-mentioned control housing part, in which the output member is held by way of a retaining ring screwed to the movable wall. For this reason, a tandem-type design would be possible only by very great structural efforts.
Another disadvantage is the considerable overall axial length and the comparatively high weight of the referenced actuating unit. The high weight is mainly due to the massive carrying pipe, made of metal, and the diaphragm plate, forming the movable walls which must be made of a thick material in order to transmit major boosting forces.
Finally, still another disadvantage is that the configuration of the carrying pipe depends on customer requests for flange patterns or vehicle-related flange patterns to mount the master brake cylinder to the booster housing and to mount the brake power booster to the vehicle body wall. Different carrying pipes are required for different combinations of flange patterns.
Therefore, an object of the present invention is to provide an actuating unit of the previously mentioned type with a design which permits reducing costs and weight. In addition, both the booster housing and the diaphragm plate should be made of an extremely thin sheet metal. Further, the application of control assemblies, which nowadays are typically rated for a plurality of booster sizes, with almost all component parts and in particular those requiring tools should be ensured without structural modifications. Still further, the invention is to provide a simple and inexpensive tandem-type design.
This object is achieved according to the present invention in that the force-transmitting element is a continuous bolt which extends in an axial direction through the control housing.
As in the past, the vacuum forces acting on the booster housing half closest to the vehicle body wall and the forces which are developed by a possible pulling of the actuating pedal or by an abrupt resetting movement of the brake pedal, are introduced into the vehicle body wall. All the other occurring forces are absorbed and transmitted by the central bolt under pressure and tension which does not depend on the desired flange pattern.
Due to a favorable improvement provided by the present invention, the operating safety is increased by means of the valve piston having a sleeve-shaped design. The sleeve-shaped valve piston is guided on the bolt and, with its end, supported at the actuating pedal. The preferred embodiment provides a large guide length for the valve piston so that the buckling risk is eliminated as far as possible.
Another embodiment of the present invention, in which the brake power booster includes an elastic reaction disc which is arranged in the control housing and permits transmitting the output force of the brake power booster to the piston by means of a pressure plate being in force-transmitting connection with a piston guided in the master brake cylinder, includes a reaction disc and pressure plate that have an annular design and are positioned coaxially relative to the bolt on a sleeve, which is slidably guided on the bolt. This reduces the response/resetting force hysteresis.
In another embodiment of the present invention, which can be produced in a particularly cost-efficient way, the output force is transmitted to the piston by means of at least two rod-shaped elements which are arranged symmetrically in parallel to the bolt between the piston and the pressure plate.
An improvement of the piston guide is achieved, according to another embodiment of the present invention, in that the output force is transmitted to the piston by means of a bolt-shaped element which is guided in a hollow-cylindrical section of the bolt having radially opposed slots, and which is in axial abutment against a pin positioned perpendicularly in the pressure plate. The bolt-shaped part can preferably be formed by an axial extension of the piston.
In still another embodiment of the present invention, the end of the bolt which is associated with the master brake cylinder is connected to a closure element closing the master brake cylinder towards the outside. This allows a direct transmission of the reaction forces from the master brake cylinder to the vehicle body wall, without an additional deviation.
In the preferred embodiment of the present invention, the pneumatic forces, acting on the booster housing half closest to the master brake cylinder and depending on the vacuum, are directly transmitted to the vehicle body wall by connecting the end of the bolt associated with the master brake cylinder to a bowl-shaped part which receives the end of the master brake cylinder housing projecting into the booster housing and is connected to the booster housing half closest to the master cylinder.
The bowl-shaped part preferably has a radial collar which serves to fasten the part to the booster housing and as an abutment for a resetting spring biasing the movable wall in opposition to the actuating direction, so that a good guide of the resetting spring is ensured. A cost-effective simplification of the construction is provided by the bowl-shaped part being formed in one part with the booster housing half closest to the master cylinder.
In a further embodiment of the present invention, the torsional stiffness of the actuating pedal is increased by the actuating pedal being of fork-shaped design and including two parallel arms spaced from each other, the bolt extending between the arms. By this means it is possible to realize a solid actuating pedal without excess weight in comparison with conventional brake pedals.
The mounting of the actuating unit according to the present invention is considerably simplified because the actuating pedal is pivotally supported at a pedal assembly mounted on the booster housing, in which the fastening means associated with the vehicle body wall is provided at the periphery of the booster housing. This allows furnishing complete assemblies which can be mounted into automotive vehicles by the automotive vehicle manufacturers without causing additional costs.
A further embodiment of the present invention provides an optimal utilization of the mounting space available in the automotive vehicle in that the actuating unit, in the mounted condition on the vehicle body wall, is clamped in between the booster housing and the pedal assembly.
Furthermore it is particularly preferable, when the end of the bolt remote from the master brake cylinder is anchored at the pedal assembly. This is a simple way of transmitting all the forces to the vehicle body wall through the bolt.
A shortening of the empty run occurring during actuation, which is important for the function, is achieved by providing a transverse member which defines the inactive position of the valve piston and is in axial abutment against a ring seal sealing the booster housing towards the outside.
Further details, characteristics and advantages of the present invention will become apparent to those skilled in the art from the subsequent description of the preferred embodiment.